# The Crossref Curriculum

## Tips for creating a DOI suffix

• Be concise: Make the suffix short and easy to read. Remember, DOIs will appear online and in print; users will also re-type DOIs.
• Be unique: A suffix must be unique within your prefix.
• Be case insensitive: A suffix is case insensitive, so 10.1006/abc is the same as 10.1006/ABC.
• Be consistent: The suffix should reflect a consistent, logical system that can be easily recorded and understood by employees of your organization. For example, you might want the suffix to include existing internal identifiers.
• Avoid page numbers: choosing a pattern that is linked to page numbers makes it difficult to put content online before pagination is complete for a print version, or if the items are published online only.
• Only use approved characters: Your DOI suffix can be any alphanumeric string, using the approved characters “a-z”, “A-Z”, “0-9” and “-._;()/” You might see some older (pre-2008) DOIs which contain other characters.
• Make suffixes extensible: DOI suffixes should be extensible, to allow DOIs to be assigned to parts of a content item, such as figures, graphs, and supplementary materials. In an example article with DOI 10.1006/jmbi.1998.2354, the second figure in the article might be assigned this DOI: 10.1006/jmbi.1998.2354.f002

Last Updated: 2020 April 8 by Laura J. Wilkinson